Query regarding One Linux command

ulimit -a gives the following output:
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 1033416
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8 ..


1.Can you suggest how we can check the current open file count in our system?
2. Do we have a way to increase the open file count on our system?
3.Is it possible that open files count increasing beyond 1024can cause some issue ?

Regards
Abhishek Saha